Significant progress has been made in understanding the pathophysiology of neuronal death in the mature brain. Much less is known about the pathophysiology of injury to the developing brain. One of the most important injuries is periventricular leukomalacia (PVL). PVL is a common cause of cerebral palsy in the premature infant. Two widely accepted potential etiologies for the pathogenesis of PVL are hypoxia-ischemia and cytokine toxicity. A window of developmental vulnerability appears to exist when either insult may result in death of oligodendrocyte (OL) progenitors whose differentiation into mature OLs is critical for myelin formation. The cellular basis for this vulnerability is unknown, but recent data indicates that some types of OL death may be apoptotic and that either hypoxia-ischemia or cytokines may lead to OL death via a mechanism triggered by oxidative stress. We have recently shown that OL death can be caused by a glutamate uptake-mediated mechanism which depletes intracellular glutathione. Glutamate toxicity can be prevented by cystine, a precursor for glutathione. Cystine deprivation is equally toxic to OLs, supporting a general mechanism of death triggered by oxidative stress. OL progenitors are particularly vulnerable to these toxic insults suggesting an explanation for the developmental specificity of PVL. We will test the hypothesis that a developmental vulnerability to "oxidative stress" is an important mechanism of OL toxicity in developing white matter. The principal model of oxidative stress is OL death induced by cystine deprivation. Oxidative stress will be characterized in terms of the relationship of glutathione depletion to the accumulation of oxygen radicals which may trigger OL death. We will employ stage-specific OL markers to determine which OL developmental stages are vulnerable to death and whether death occurs via apoptosis in tissue culture and in human perinatal autopsy tissue showing pathological evidence for perinatal white matter injury. At the conclusion of his training, the principal investigator will have acquired a foundation in molecular and cell biology and in human neuropathology to begin to address the broader biological relevance of the mechanism of OL death for the pathophysiology of PVL. From the results of these studies, we hope to determine intrinsic features of the OL progenitor which influence the vulnerability to death from oxidative stress, and thereby, gain access to strategies to prevent PVL. The specific aims of this project are: l. Employ immunocytochemical markers to define in vitro the oligodendrocyte developmental stages which are most vulnerable to death by oxidative stress. 2. Characterize in vitro the role of oxidative stress in oligodendrocyte death. 3. Determine in vitro whether oligodendrocyte death by oxidative stress occurs by apoptosis. 4. Determine whether specific oligodendrocytes phenotypes die by apoptosis in vitro and human brain.